1,720,973 research outputs found
Onset of entanglement and reptation in melts of linear homopolymers: consistent rheological simulations of experiments from oligomers to high polymers
Full text linkThe shear rheological behavior is investigated in this work for a series of poly(ethyl acrylate) samples, whose molar mass ranges from oligomers to high polymers. The focus was on studying the
onset of entanglement effects over selected reptation models in order to ascertain their ability to reproduce the complex shear modulus of the polymers and to provide consistent values of the
microscopic parameters driving the structural relaxation of the polymer system.
Among ordinary reptation topological models, we found that, the Doi–Edward model, implemented with contour length fluctuation and constraint release mechanism for the tube relaxation, better
reproduced the rheological response of the materials. Most importantly, we were able to simulate material functions to obtain consistent microscopic information on the materials, such as Rouse
time and entanglement molar mass, over the whole range of investigated molar masses, therefore overcoming the discrepancy usually found, mostly in the mass region of partial entanglement.
Finally, descriptions of the polymer entanglement features, in agreement with the experimental and microscopic model findings, are provided in the framework of the packing-length phenomenological model, and by means of analytical calculations of the polymer viscosity according to the Milner–McLeish–Likhtman model
Design, construction and testing of a microwave cavity for linear and non-linear ESR spectroscopy at 4.5 GHz operating in TE0102 mode
No full textIt was proved that the combined use of linear and non-linear electron spin resonance (ESR) spectroscopy is
able to enlighten the non-exponential behaviour of the reorientational correlation function of spin probes dissolved
in complex systems. In these systems the structural relaxation is expected to depend on the frequency excitation,
therefore it seems useful to extend the investigation at frequencies other than the standard 9.8 GHz. In the present
work, the design, the manufacturing, the characterisation of a rectangular cavity operating in TE102 mode at 4.5
GHz, and its coupling to a WR187 waveguide through an iris tuner, are carefully described. Its performance when
loaded with large lossy samples has also been tested and compared with the performances of the X-band TE102,
TM110, and theoretical TEU02 cavities
Comparison of the Viscoelastic Behavior of Side-Chain Liquid Crystal Azobenzene Block and Random Copolymer
No full textModeling and Predicting the Viscoelastic Behavior of Side-Chain Liquid Crystal Azobenzene Homopolymers and Random Copolymers
No full text
Analysis of environmental damage consequences on viscous thermo elastic properties of a polymer interlayer
No full textStructural response of laminated glass elements is heavily influenced by the visco-thermo-elastic properties of polymer interlayer. Mechanical characterization of such polymers can be carried out with different experimental procedures such as creep tests, relaxation tests (both named transient tests) or tests with load or displacement periodically imposed. In the linear viscoelastic domain, mechanical parameters determined with such methods, are usually extended to time and frequency domain wider than the experimental one, translating the experimental points in the space of time or temperature, according to the time-temperature superposition principle. An incautious use of this procedure does not account for structural modifications that the polymer can suffer due to environmental actions such as solar radiation, temperature variations and moisture absorption. Here we describe the first results of an experimental campaign carried out with periodic tests on laminated glass specimens some of which previously exposed to moisture accelerated aging
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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